A harmonic oscillator, also called a dielectric resonator, has advantages such as a high permittivity and a low electromagnetic loss, and is widely applied in a variety of microwave radio frequency devices, for example, a cavity filter and a duplexer constituted by a cavity filter. Generally, the harmonic oscillator is of a cylinder shape and is formed by a microwave dielectric ceramic by means of integrated sintering.
The microwave dielectric ceramic also has an advantage such as a high permittivity, a low electromagnetic loss, and high withstanding power, and therefore meets a requirement of the harmonic oscillator. However, with the development of science and technology and continuous improvement of product integration, people have an increasing demand for filter and duplexer miniaturization. In the prior art, a volume of a cavity filter and a volume of a duplexer are in inverse proportion to a resonance frequency. If a volume of a resonant cavity of the cavity filter or duplexer is directly reduced, a resonance frequency corresponding to the cavity filter or duplexer will increase, so that a filtering function requirement of the filter cannot be met. How to implement miniaturization without affecting a normal use function of a cavity filter and a duplexer is an issue that needs to be urgently solved now by research and development personnel together.